OpenStack Nova 之使用SQLAlchemy 操作 Mysql 示例

SQLAlchemy 简介 【链接】

The SQLAlchemy Object Relational Mapper presents a method of associating user-defined Python classes with database tables, and instances of those classes (objects) with rows in their corresponding tables. It includes a system that transparently synchronizes all changes in state between objects and their related rows, called a unit of work, as well as a system for expressing database queries in terms of the user defined classes and their defined relationships between each other.

我的理解是，SQLAlchemy 是实体/关系映射的一种操作数据的方式， 实体是由Python所编写的类， 这个类的每一个实体，就对应于数据库中的每一条元组（行数据）。其中对这个类的实体的操作，直接映射（影响）到数据库中对应的元组， 这种方式叫做 工作单元（操作单元，有点类似于一个原子操作把）

自己写的查询Flavor 的样例

from sqlalchemy.orm import sessionmaker
from sqlalchemy import create_engine
from sqlalchemy.ext.declarative import declarative_base
from sqlalchemy import Column, Integer, String, Float, Boolean

sql_connection = "mysql://root:root@localhost/nova?charset=utf8"
engine = create_engine(sql_connection, echo=True) #echo=True 设置该项后，可以打印出sql的执行过程
Session = sessionmaker(bind=engine)
session = Session()

class NovaBase():
pass

BASE = declarative_base() # 用户创建与DB映射的基类

class InstanceTypes(BASE, NovaBase):
__tablename__ = "instance_types" # 数据库中表的名称
id = Column(Integer, primary_key=True) #Column 用于定义数据表 "instance_types”的字段， 其参数是该字段的具体的类型
name = Column(String(255))
memory_mb = Column(Integer)
vcpus = Column(Integer)
root_gb = Column(Integer)
ephemeral_gb = Column(Integer)
flavorid = Column(String(255))
swap = Column(Integer, nullable=False, default=0)
rxtx_factor = Column(Float, nullable=False, default=1)
vcpu_weight = Column(Integer, nullable=True)
disabled = Column(Boolean, default=False)
is_public = Column(Boolean, default=True)

flavors = session.query(InstanceTypes).all() #查询数据表
for flavor in flavors:
print flavor.id, flavor.name

代码输出

2013-05-15 18:41:10,928 INFO sqlalchemy.engine.base.Engine SELECT DATABASE()
2013-05-15 18:41:10,929 INFO sqlalchemy.engine.base.Engine ()
2013-05-15 18:41:10,933 INFO sqlalchemy.engine.base.Engine SHOW VARIABLES LIKE 'character_set%%'
2013-05-15 18:41:10,934 INFO sqlalchemy.engine.base.Engine ()
2013-05-15 18:41:10,935 INFO sqlalchemy.engine.base.Engine SHOW VARIABLES LIKE 'lower_case_table_names'
2013-05-15 18:41:10,936 INFO sqlalchemy.engine.base.Engine ()
2013-05-15 18:41:10,937 INFO sqlalchemy.engine.base.Engine SHOW COLLATION
2013-05-15 18:41:10,937 INFO sqlalchemy.engine.base.Engine ()
2013-05-15 18:41:10,946 INFO sqlalchemy.engine.base.Engine SHOW VARIABLES LIKE 'sql_mode'
2013-05-15 18:41:10,946 INFO sqlalchemy.engine.base.Engine ()
2013-05-15 18:41:10,948 INFO sqlalchemy.engine.base.Engine BEGIN (implicit)
2013-05-15 18:41:10,950 INFO sqlalchemy.engine.base.Engine SELECT instance_types.id AS instance_types_id, instance_types.name AS instance_types_name, instance_types.memory_mb AS instance_types_memory_mb, instance_types.vcpus AS instance_types_vcpus, instance_types.root_gb AS instance_types_root_gb, instance_types.ephemeral_gb AS instance_types_ephemeral_gb, instance_types.flavorid AS instance_types_flavorid, instance_types.swap AS instance_types_swap, instance_types.rxtx_factor AS instance_types_rxtx_factor, instance_types.vcpu_weight AS instance_types_vcpu_weight, instance_types.disabled AS instance_types_disabled, instance_types.is_public AS instance_types_is_public
FROM instance_types
2013-05-15 18:41:10,950 INFO sqlalchemy.engine.base.Engine ()

1 m1.medium
2 m1.tiny
3 m1.large
4 m1.xlarge
5 m1.small
6 m1.nano
7 m1.micro

　　

Nova 中所对应的代码结构

nova/openstack/common/db/sqlalchemy/models.py 定义了SQLAlchemy 的基类， 所有的对数据的操作，通过该类中定义的方法来实现， 其子类，只需要调用相关的方法即可

nova/db/sqlalchemy/models.py 定义了nova数据中的所有的表

以InstanceTypes 为例

BASE = declarative_base() # 与上一个类子中的方法一样

class NovaBase(models.SoftDeleteMixin, models.ModelBase): #区别在这里， models 为1中定义的模块
pass

class InstanceTypes(BASE, NovaBase):
__tablename__ = "instance_types" # 数据库中表的名称
id = Column(Integer, primary_key=True) #Column 用于定义数据表 "instance_types”的字段， 其参数是该字段的具体的类型
name = Column(String(255))
memory_mb = Column(Integer)
vcpus = Column(Integer)
root_gb = Column(Integer)
ephemeral_gb = Column(Integer)
flavorid = Column(String(255))
swap = Column(Integer, nullable=False, default=0)
rxtx_factor = Column(Float, nullable=False, default=1)
vcpu_weight = Column(Integer, nullable=True)
disabled = Column(Boolean, default=False)
is_public = Column(Boolean, default=True)